In communication systems or networks, messages are transmitted by a sender to one or more receivers. The transmission media and protocols used for transmitting the messages depend on the particular design of the communication system. Examples of communication systems are radio communication systems such as cellular mobile radio communication systems or WLANs (Wireless Local Area Networks), or line-based communication systems such as the public telephone network or LANs (Local Area Networks) or corporate communication networks.
Communications between communication terminals are possible both within a communication network as well as between communication terminals of different communication systems. If a node of a first network initiates the establishment of communication with a node of a second communication network, from the point of view of the first network this constitutes an outgoing communication. If, on the other hand, a node of the second network initiates the establishment of communication with a node of the first network, from the point of view of the first network this constitutes an incoming communication. The establishment of a communication is usually performed by exchanging appropriate signaling messages.
The document US 2002/0143855 A1 describes a peer system in which two groups of peers exist, in which peers in one group cannot communicate directly with peers in the other group. There is a relay node which forwards messages between the two groups.
The document US 2004/0260761 Al describes a peer-to-peer network for identifying devices. For this purpose, each device enters an identification file in the peer-to-peer network, which file can be searched and filtered by a search engine in order to determine suitable partners.
The document DE 103 24 372 Al describes the registration of a terminal on a communication node of a communication network. For this purpose the terminal accesses an information store in which the communication nodes are registered.
The document “Newton, Harry: Newton's Telecom Dictionary, 20th updated and expanded edition, San Francisco, Calif., USA: CMP Books, March 2004, page 754, dictionary entry for “Skype”, ISBN 1-57820-309-0”, describes Skype, software which enables PCs to exchange voice communications over the internet. Skype utilizes VoIP and peer-to-peer technology.